ffmpeg从流mp4中提取音频

我试图从流mp4中提取音频，它成功了

ffmpeg -i http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_1mb.mp4 out2.mp3

但它在这个 facebook mp4流媒体视频上失败了。（辣妹警报）

它抛出错误： out2.mp3: command not found

我怀疑ffmpeg强制我有文件扩展名？

ffmpeg -i https://scontent.xx.fbcdn.net/v/t42.9040-29/10000000_1730984783818335_416671574_n.mp4?efg=eyJ2ZW5jb2RlX3RhZyI6InNkIn0=&oh=e720dd84a1bb46a272bf748a93b597b9&oe=57CB4994 3.mp3

控制台输出：

 [1] 4940
    [2] 4941
    -bash: 3.mp3: command not found
    [2]+  Done                    oh=e720dd84a1bb46a272bf748a93b597b9
    ffmpeg version 3.1.3 Copyright (c) 2000-2016 the FFmpeg developers
      built with Apple LLVM version 7.3.0 (clang-703.0.31)
      configuration: --prefix=/usr/local/Cellar/ffmpeg/3.1.3 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-opencl --enable-libx264 --enable-libmp3lame --enable-libxvid --disable-lzma --enable-vda
      libavutil      55. 28.100 / 55. 28.100
      libavcodec     57. 48.101 / 57. 48.101
      libavformat    57. 41.100 / 57. 41.100
      libavdevice    57.  0.101 / 57.  0.101
      libavfilter     6. 47.100 /  6. 47.100
      libavresample   3.  0.  0 /  3.  0.  0
      libswscale      4.  1.100 /  4.  1.100
      libswresample   2.  1.100 /  2.  1.100
      libpostproc    54.  0.100 / 54.  0.100

由我自己解决，只是在网址上引用